K. Lynn, P. E. Yankwich
1962
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Journal
Biochimica et biophysica acta
Abstract
The 13C kinetic isotope effects in the urease-catalyzed hydrolysis of urea have been measured with several preparations of the enzyme in two buffers (maleic acid-maleate, and Tris-sulfuric acid) in which the kinetics have been studied previously. The results indicate that the mechanism of the hydrolysis possesses complexities not reflected in the gross rate phenomena which do influence the isotope fractionation. The isotopic analogues of the several mechanisms found adequate to explain the kinetics of the reaction are examined in detail. It is concluded that complexity at the molecular level, probably involving temperature-dependent interconversion of two or more types of active sites (directly, or indirectly through enzyme conformational changes), is responsible for the isotope-effect results obtained.